4.4 Elements in Group 17

Short Answer Questions

1. What is another name for the elements in Group 17 of the periodic table?
   Answer
   Halogens.
2. Name the five halogens.
   Answer
   Fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).
3. How many valence electrons do halogens have?
   Answer
   Seven.
4. Do halogens exist as single atoms or molecules?
   Answer
   Diatomic molecules (F₂, Cl₂, Br₂, I₂, At₂).
5. Are halogens generally reactive or unreactive?
   Answer
   Very reactive.
6. How does the reactivity of halogens change as you go down the group?
   Answer
   It decreases.
7. What is the state of fluorine at room temperature?
   Answer
   Gas.
8. What is the state of bromine at room temperature?
   Answer
   Liquid.
9. What is the state of iodine at room temperature?
   Answer
   Solid.
10. What colour is chlorine gas?
    Answer
    Green-yellow.
11. What type of ion do halogens typically form?
    Answer
    Negative ions (anions).
12. Do halogens gain or lose electrons to form ions?
    Answer
    Gain electrons.
13. How do halogens react with metals?
    Answer
    They form metal halides.
14. How do halogens react with hydrogen?
    Answer
    They form hydrogen halides.
15. Is fluorine more or less reactive than iodine?
    Answer
    More reactive.
16. Are halogens good or poor conductors of electricity?
    Answer
    Poor conductors.
17. How does atomic size change as you move down Group 17?
    Answer
    It increases.
18. What is the name given to the reaction between a metal and a halogen?
    Answer
    A metal halide.
19. What is the name given to the reaction between hydrogen and a halogen?
    Answer
    A hydrogen halide.
20. What is the oxidation state (charge) of a halogen ion?
    Answer
    -1.

Explanation Questions

1. Explain why halogens are so reactive.
   Answer
   Halogens are highly reactive because they have seven valence electrons, needing only one more to achieve a stable electron configuration (octet). This means they readily gain an electron from other elements to form a negative ion, making them very reactive with other elements.
2. Why does the reactivity of halogens decrease down the group?
   Answer
   As you go down Group 17, the atomic size increases due to the addition of extra electron shells. The valence electrons are further from the nucleus and are shielded by more inner electrons, reducing the attractive force of the nucleus. This makes it more difficult to attract another electron to the outer shell. Hence, the reactivity decreases down the group.
3. Describe the general reaction of halogens with hydrogen.
   Answer
   Halogens react with hydrogen to form hydrogen halides (e.g., hydrogen chloride, HCl). These reactions can be vigorous, especially with fluorine and chlorine. The hydrogen halides formed are acidic when dissolved in water.
4. Explain why halogens exist as diatomic molecules.
   Answer
   Halogen atoms have seven valence electrons, so they are one electron short of a stable outer shell (octet). To achieve stability, two halogen atoms share electrons to form a covalent bond, thus creating a diatomic molecule, for example, Cl₂.
5. Why do halogens have relatively low melting and boiling points?
   Answer
   Halogens have low melting and boiling points because they are simple molecular substances with weak intermolecular forces (van der Waals' forces) between the molecules. Only a small amount of energy is required to overcome these forces and change their state. However, the strength of the van der Waals' forces increases with molecular size, explaining why boiling and melting points increase down the group.
6. How do halogens form ions?
   Answer
   Halogens form negative ions (anions) by gaining one electron to complete their outer shell and achieve a stable electron configuration. This results in a -1 charge, with the number of electrons then being equal to the number of protons plus one.
7. Compare the reactions of fluorine, chlorine, and bromine with hydrogen.
   Answer
   Fluorine reacts very vigorously and explosively with hydrogen, even in the dark, forming hydrogen fluoride. Chlorine reacts rapidly with hydrogen, but requires light or heat to initiate the reaction, forming hydrogen chloride. Bromine reacts much less vigorously with hydrogen and requires a higher temperature, forming hydrogen bromide. The general trend is, therefore, that the reactivity with hydrogen decreases down the group.
8. Explain why the atomic size of halogens increases down the group.
   Answer
   As you move down Group 17, each element has an additional electron shell. This increased number of electron shells results in a larger atomic radius and a larger overall atomic size, as the outermost electrons are further from the nucleus.
9. How does the reaction between a metal and a halogen result in a stable compound?
   Answer
   Metals tend to lose electrons and halogens tend to gain electrons in order to obtain a full outer shell of electrons. When a metal reacts with a halogen, the metal atom loses electrons to the halogen atom. This results in the formation of oppositely charged ions (cations and anions), which attract each other to form an ionic compound with a giant ionic lattice structure.
10. Why are halogens poor conductors of electricity?
    Answer
    Halogens are poor conductors of electricity because they exist as diatomic molecules with covalent bonds. These molecules do not have free electrons that can move to carry an electrical charge in the structure. The bonding in halogens results in molecules with all electrons held in place by covalent bonds rather than being delocalised throughout the structure.